Nowadays, machines for gluing the final edge of logs, fed one after the other, are known.
Such machines commonly comprise in succession, i.e. following the advancing direction of the logs, a station for unwinding the logs in which the final edge is identified, a station in which such an edge is held and a station in which the log receives the glue at an inner layer of paper with respect to that defined by the final edge.
Some known machines also comprise a station, downstream of the dispensing station of the glue, for rewinding the final edge on the log where, thanks to the glue transferred in the previous station, the final edge is fixed to the rest of the log.
Without such a rewinding station the edge is fixed to the rest of the log by simply advancing by rolling of the log itself downstream of the glue dispensing station.
The stations in which the final edge is held upstream of the glue dispensing station comprise a suction element which has the purpose of holding the final edge moving it away from the log for a predetermined length before glue is dispensed on the log itself.
Of course, in order to ensure such an aforementioned operation, it is necessary for the final free edge of the log to come into contact with the suction element.
Indeed, otherwise, i.e. no contact of the final edge with the suction element, it could happen that the edge is not moved away from the log and consequently glue is dispensed on the outer surface of the log itself.
Disadvantageously, in such conditions, the final edge is not glued onto the log and glue is spread on the parts of the machine that could also ruin the following logs.
As well as ensuring the contact of the final edge with the suction element, there is a further advantage if the first contact of the log with the suction element occurs right at such a final edge, that is to say, if the log reaches the suction element timed with the edge arranged at “6 O'clock”.
Indeed, in this case, the time the suction element is “occupied” by the log is reduced to the minimum thus optimizing the production of finished logs per hour.
Analysing the operation of moving away the final edge, it requires an unavoidable period of time, which starts with the contact of the final edge with the suction element and ends when it has reached a predetermined length away from it, as well as a possible time for the suction element to “search” for the edge.
It should be clear that such a time searching for the edge is an unnecessary waste of time and it slows down production.
In particular, the time searching for the edge occurs when the first contact with the suction element does not occur at the final free edge, delaying the moment when the predetermined distance away of the edge itself has been reached, at which the log is made to advance on the glue dispenser.
In order to ensure that the first contact of the log with the suction element occurs at the final edge, known machines comprise devices called “timing devices” arranged upstream of the suction element which have the special function of arranging the final edge on the log in a particular angular position according to the diameter of the log and to the distance between the timing devices themselves and the suction element.
As the diameter of the log varies, the timing means must impose on the final edge a different particular angular position before making it advance so as to always ensure that the first contact of the log with the suction element occurs at the final edge itself.
In a first known embodiment such timing means comprise a pair of rollers or belts arranged between the unwinding station and the gluing station.
In other known embodiments, the timing means are integrated in the unwinding station and comprise photocells and suitably oriented blowing elements.
However, both aforementioned solutions have some drawbacks. Indeed the presence of rollers or belts between the unwinding station and the gluing station necessarily increases the time needed for the processing of the single logs, whereas, unwinding stations integrated with the timing means slow down the production of the finished logs per hour holding the single logs also for the time required by the aforementioned timing.